1. Field of the Invention
The present invention relates to the synthesis of azines and to the production of hydrazine hydratetherefrom.
2. Description of the Prior Art
Hydrazine, which typically exists in the form of hydrazine hydrate, is a compound which is very widely used, inter alia, as an intermediate for numerous syntheses. According to Kirk Othmer, 3rd edition, volume 12, pages 734 to 755, hydrazine is produced either by the oxidation of ammonia using chlorine or bleach and optionally a ketazine intermediate, or by the reaction of hydrogen peroxide, ammonia and a ketone.
The peroxide process has been described in numerous patents, in particular U.S. Pat. Nos. 3,972,878, 3,972,876, 3,869,541, 3,948,902, 3,919,256, 3,943,152 and 4,093,656. Kirk Othmer, supra, describes the principle of the process according to U.S. Pat. No. 4,093,656. Thus, hydrogen peroxide, ammonia and methyl ethyl ketone are reacted in the presence of acetamide and sodium phosphate to prepare, after separation, the corresponding azine and an aqueous solution (the working solution) containing acetamide and sodium phosphate. This aqueous solution is concentrated to remove the water produced by the reaction, as well as the water contributed by the hydrogen peroxide, and then is recycled to the reactor. The azine is hydrolyzed to hydrazine, and the methyl ethyl ketone is recovered and recycled to the reactor (for the synthesis of the azines).
When such a process is carried out continuously, a lessening of activity is observed in the working solution or reaction medium, i.e., a lowering of productivity of the reactor, and it is thus necessary to formulate a new working solution (reaction medium).
U.S. Pat. No. 4,093,656 describes several examples of different working solutions.
In the prior art noted above, it is indicated that, although the process of azine synthesis can be carried out using the reagents in widely varying proportions, variations in the production yield of azines can be observed. Hence, it is advantageous to maintain certain proportions in the reaction mixture, in particular for the compounds contained in the working solution.
Accordingly, a major object of the present invention is the provision of an improved process for the preparation of azines, which improved process is far simpler than those to date characterizing the state of this art and which permits of the continuous and constant production of azine without requiring stringent monitoring of the working solution (reaction medium).
Briefly, the present invention features a process for the synthesis of azines from hydrogen peroxide, ammonia and a reagent having a carbonyl group, comprising:
(a) contacting such reagents with a solution, designated the working solution or reaction medium, until the azine is produced;
(b) (i) separating the azine and optionally the excess of carbonylated reagent from (ii) the working solution;
(c) increasing the temperature of all or a portion of the working solution to a value greater than 130xc2x0 C., with the water produced by the reaction being eliminated either before, after or concomitantly with such temperature increase;
(d) recycling the working solution to step (a); and
(e) introducing a compound adapted to maintain the production of the azine into the working solution during at least one of the above steps (a) to (d).